The present invention relates to a process for producing xcex5-caprolactam from cyclohexanone oxime and an apparatus for the process.
xcex5-caprolactam may be used as a monomer for producing Nylon-6, that is a raw material for producing fibers, engineering plastics and the like. xcex5-caprolactam may be produced by a process in which cyclohexanone oxime is evaporated and is then rearranged into xcex5-caprolactam in a gas phase Beckmann rearrangement reaction. Heretofore, however, the process has problems such that xcex5-caprolactam is produced with a relatively high content of by-products such as cyanopentenes, octahydrophenazine and caprenolactam.
For example, United Kingdom (GB) Patent No. 999,851 discloses a process in which cyclohexanone oxime is evaporated in a fluidized bed of an acidic catalyst and is then rearranged into xcex5-caprolactam using an acidic catalyst. In this process, however, a part of cyclohexanone oxime is decomposed to be cracking products, which results in lowering the purity of the resulting xcex5-caprolactam. The GB Patent also discloses a process comprising two steps of evaporating cyclohexanone oxime in a falling film evaporator and rearranging the evaporated cyclohexanone oxime in a reactor. This process, however, is insufficient in suppressing the generation of the cracking products.
On the other hand, German Patent 2,641,414 (corresponding to U.S. Pat. No. 4,137,263) discloses an improved method for evaporating cyclohexanone oxime in a falling film evaporator. This process, however, is also insufficient in suppressing the generation of the cracking products since a large amount of cyclohexanone oxime is circulated in the evaporator at high temperature. Also, it is difficult to control evaporation conditions in the evaporator in an industrial scale.
One objective of the present invention is to provide a process for producing xcex5-caprolactam with sufficiently reducing the generation of by-products. The present inventors have found that this object and other objects are achieved by a process comprising the steps of evaporating a mixture of cyclohexanone oxime and a solvent in a fluidized bed and rearranging the cyclohexanone oxime into xcex5-caprolactam, and have accomplished the present invention.
The present invention provides a process for producing xcex5-caprolactam comprising the steps of evaporating a mixture of cyclohexanone oxime and a solvent by introducing the mixture into a fluidized bed in which inert particles are fluidized by an inert gas, the particles having heat enough to evaporate the mixture; and rearranging cyclohexanone oxime in the evaporated mixture into xcex5-caprolactam by a gas phase Beckmann rearrangement reaction using a solid catalyst, excluding a catalyst consisting of a boric acid or a boron oxide.
The present invention also provides an evaporator, comprising an evaporation column in which inert particles are fluidized; a pipe for introducing a mixture of cyclohexanone oxime and a solvent into the column; and a heat source for providing the inert particles with heat enough to evaporate the mixture, the heat source being installed at the inside and/or outside of the column.
The present invention further provides an apparatus, comprising an evaporation zone (or evaporator) in which a mixture of cyclohexanone oxime and a solvent is evaporated in a bed of inert particles which are fluidized by an inert gas, the particles having heat enough to evaporate the mixture; and a reaction zone (or reactor) in which cyclohexanone oxime in the evaporated mixture is rearranged into xcex5-caprolactam by a gas phase Beckmann rearrangement reaction using a solid catalyst, excluding a catalyst consisting of a boric acid or a boron oxide.